How is exercise testing useful in determining the prognosis of chest pain ?

How is exercise testing useful in determining the prognosis of chest pain ?
 
A study at Duke University used exercise testing to determine high- and Iow-risk subsets in patients with chest pain suggestive of ischaemic heart disease:
 
• Low-risk subset: subjects who could complete 9 minutes of exercise using the Bruce protocol without evidence of ischaemic ST segment changes and achieve a maximal sinus heart rate in excess of 160 beats per minute. These were found to have a l-year survival rate of 99% and a 4-year survival rate of 93%. This .means that cardgac ,.:atheterixation and CABG ,:an be deferre,J.
 
• High-risk subset: those who were forced to stop exercising in stages I or Il (under 6 minutes);survival rate was 85% at I year and 63% at 4 years.

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